package DataStructures.Sort;

/**
 * Created by 其 on 2016/4/19.
 */
public class MergeSort {
    public MergeSort(int[] a){
        sort(a,0,a.length-1);
    }
    private void sort(int[] data, int left, int right) {
        if(left < right){
            //找出中间索引
            int center = (left+right)/2;
            //对左边数组进行递归
            sort(data, left, center);
            //对右边数组进行递归
            sort(data, center+1, right);
            //合并
            merge(data, left, center, right);
        }
    }
    private void merge(int[] data, int left, int center, int right) {
        int [] tmpArr = new int[data.length];
        int mid = center+1;
        //third记录中间数组的索引
        int third = left;
        int tmp = left;
        while(left<=center && mid<=right){
            //从两个数组中取出最小的放入中间数组
            if(data[left] <= data[mid]){
                tmpArr[third++] = data[left++];
            }
            else{
                tmpArr[third++] = data[mid++];
            }
        }
        //剩余部分依次放入中间数组
        while(mid <= right){
            tmpArr[third++] = data[mid++];
        }
        while(left <= center){
            tmpArr[third++] = data[left++];
        }
        //将中间数组中的内容复制回原数组
        while(tmp <= right){
            data[tmp] = tmpArr[tmp++];
        }
    }
}
